1. Field of the Invention
The present invention relates to an optical pickup device. More particularly, the invention relates to a separation type optical pickup device which comprises an optical system for reading and writing information by scanning a recording medium with the use of a laser beam and/or for erasing the information wherein a part of the optical system is divided so that the divisional part is movable at the time of the scanning or erasing operation.
2. Description of the Related Art
In an optical information recording device, data pits are formed on a recording disk to write information thereon and the recorded information is read by scanning the row of data pits. Such a recording device comprises an optical pickup device which converges a scanning laser beam on the recording surface of the disk and also guides the reflection rays reflected from the disk surface to a photoelectric transducer to read information from the pits formed on the disk surface.
In accordance with an example of such an optical pickup device, a part of the optical system is divided so that the divisional part can be separated from the laser source portion and freely moved independently. This separation type pickup device primarily comprises an optical pickup device body housing a semiconductor laser source therein and a movable light guide system which reflects and transmits the laser beam from the laser source to the optical information recording medium in the form of a disk as well as converges the beam on the disk surface.
The device body is fixed to the body frame of an optical information read/write apparatus and comprises the semiconductor laser beam, a polarization beam splitter, a quarter-wave plate and an optical detector element.
On the other hand, the light guide system is movable on the body frame in the radial direction of the disk in the state of being faced to the recording surface of the disk. The guide system comprises an objective lens for converging the beam on the disk surface and a deflection prism for changing the direction of the optical path of the laser beam output from the laser source in the device body side toward the objective condenser lens.
In accordance with the separation type optical pickup device having the above-mentioned structure, it becomes possible to reduce the weight of the movable light guide system for scanning the recording disk surface by providing only a focus servo means thereon, which makes it possible to achieve a high speed scanning operation.
However, dusts enter into the device through an opening for passing through the laser beam formed between the fixed system of the device body side and the movable system of the light guide side, which impairs the reliability of the optical function of the device.
The optical guide system moves for scanning operation so that the opening is narrow when the guide system is located in the vicinity of the fixed body while the opening becomes wide when the guide system is shifted remote from the body so that dusts are easy to enter into the device which dusts attach on the optical elements in the device and impair the function of setting the optical path or luminous intensity of the system.
In order to cope with the above-mentioned dust problem, it may be considered to enclose each of the device body and the movable guide with a cover except for the portion of the optical path. However, if the light guide system is sealingly enclosed with a cover, the pressure in the guide system may be changed along with the motion thereof, which causes misfocussing of the condenser lens.